Can someone explain me why this shouldn't be illegal?

Well, my steelman argument against regulating this repulsive shit: every time a government says it's going to regulate infotech to protect children, it almost invariably ends up having a chilling effect that ends up restricting children's access to high quality educational and medical information. Even if a law is well-intentioned and equitable, its enforcement never is.

In this case, I'm confident that whoever wrote this section, just checking their hard drive should be sufficient to send them to jail.